hwc: Support single ROI for split panels.

For panels that cannot accept commands in both the interfaces, we cannot
send two ROI's (for each half). We merge them into single ROI and split
them across lSplit for MDP mixer use. The ROI's will be merged again
finally before updating the panel in the driver.

 - Reads panel property of dual control path.
 - If dual control path not supported, merge ROI's before
   analysing for composition strategies.

Change-Id: I67e361a299dc5d1adb28b180900e24633eefc4a8
3 files changed